THE SUMMARY OF THE EXPLANATION OF THE RELATION DATABASE
at the beginning of the video part 1, there are several terms need to remember:
steps
1.relation algebra : the basic of relational algebra query language and a few of most populate operators
2.sigma operators: the function for this operator is easy for audience to get the ideas. picking some particular rows in the relations.
3. project Operators: we use mathematic sign Phi to define the specific idea,Picking the certain attributes in the relations
4.reducing the duplicates in the relations, in this gigantic field, it actually introduced some "sub- operators"(based on what I defined by myself ), like cartesian products, which mean combine two relations together. Here's a thing , the biggest difference between the cross- product and the natural join is whether the system match up with all the columns and eliminate duplicate values
5.natural join: the professor in the video used very long and tedious sentences to describe how does this operator works. however, based on my opinions, it just like cross-product with removing the duplicates automatically.
6.theta join: Sorry, I still not very clear about this operator
7.union operator: it actually has similar using method with cross product operator, the only different is it just combine all the informations vertically, and this information are in the one list.
8.different operator: using minus sign as a symbol. to abstract some particular you need you show and always using with select operator.
9.intersection operation : a basic idea we alway love to use Venn graph to illustrate it, using opposite capital U as a symbol. and can be explain by different operators.